A wireless communication system, such as a third generation partnership project (3GPP) long term evolution (LTE) system, may use Discontinuous Reception (DRX) procedures to reduce battery power consumption of a User Equipment (UE) in the system. For example, a base station in the wireless communication system may configure a DRX cycle for a UE. In some cases, a DRX cycle may include a DRX On duration and a DRX Off duration. During the DRX On duration, the UE may receive and decode a Downlink (DL) transmission. In some cases, the monitored DL transmission may be a transmission on the Physical Downlink Control Channel (PDCCH). During the DRX Off duration, the UE may turn off its radio in order to save battery power. In some cases, the UE may extend the time that the UE monitors the DL transmission beyond the configured DRX On duration based on various events, such as new data arrival, Hybrid Automatic Repeat Request (HARM) procedure, and etc. In such a case, the time that the UE monitors the DL transmission is called the DRX active time.
A Wireless Local Area Network (WLAN) may use Legacy Power Save procedure to reduce battery power consumption of a non-AP station (STA) in a WLAN power saving mode. For example, a STA may enter a power saving mode by sending a Null frame to an Access Point (AP) with the Power Management bit set. From then on, instead of immediately transmitting all data addressed to the STA, the AP may store these data in a queue associated to this STA and send a TIM message to indicate that data are buffered for the STA. The AP may transmit the TIM message in a TIM transmission period. In some implementations, the AP may transmit the TIM message by setting the TIM field in a beacon frame. The AP may keep the frame in its buffer up for a predetermined number of beacon intervals. The predetermined number of beacon intervals is called a listen interval. A STA may set the listen interval at association time. The beacon interval is configurable. A typical value of the beacon interval is 102.4 ms. Each beacon interval includes a TIM period and a TIM transmission period. A TIM message may be transmitted during a TIM transmission period. Therefore, a STA may wake up at least once within each listen interval to decode a TIM and determine whether the AP has buffered data for the STA.
To retrieve the buffered data from the AP, the STA may send a Power Save Poll (PS_Poll) frame to the AP. In response, the AP may send a first queued data to the STA. The STA may receive the queued data. If the More Data field in this frame is set, which indicates that the AP has additional buffered data, the STA may send another PS_Poll frame to the AP. The STA may continue to send PS_Poll frames to receive all the queued frames. When all the buffered data are retrieved, the STA may go back to sleep until the next listen interval. In some implementations, the Legacy Power Save may be enhanced with a Wi-Fi Multimedia (WMM) power saving mode, which uses a slightly altered signaling procedure. For example, in a WMM power saving mode, the STA may immediately move to an active mode upon receiving the first buffered frame.
Like reference numbers and designations in the various drawings indicate like elements.